Charging 12 volt storage batteries: A Question : LUSENET : TimeBomb 2000 (Y2000) Preparation Forum : One Thread

My emergency electrical system consists of a generator and two 6volt deep cycle golf cart batteries wired together for 12 volts. I have a couple of basic 300 watt inverters, a digital volt meter and a battery charger.

My intention is to run my generator for an hour or so each day to run water pump and kitchen appliances and to recharge the batteries. The battery storage will be to run a few florescent light bulbs, a dc tv, dc cd player, and a cb radio.

I'm not real familiar with batteries and charging them so have a couple of questions for those of you who know this subject real well:

1. I bought the volt meter to keep close tabs on the batteries. At what voltage can I let the batteries drop before I recharge them?

2. How high of a voltage should I recharge them up to?

3. my charger has the option of 2amp, 40 am or 200 amp charging. It does not have the ability to be set and left to shut itself off (at least that I know of--I have not used it yet). I figure that charging at 200 amps will get the job done in far less time, and with much less gas used by my generator. But is there a disadvantage to charging at 200 amps?

3. Is there anything else I should know or be asking regarding this subject?

Thanks very much for your help

-- farmbeet (farmbeet@12volt.power), November 28, 1999


1) Your batteries can by cycled to 80% of their capacity. In your case this translates to 11.58 volts (full charge is 12.70 volts)

2) Your charger should be set to charge them at a rate of 14.4-14.8 volts.

3) I'm guessing your batteries are rated at 220 amp-hours. You should be able to charge them at 200 amps for a short period of time.

someone else please chime in and correct me if I'm off on any of this or have any additional info.

also- here is one of the best Battery F.A.Q.s I have come across:


-- plonk! (, November 28, 1999.

You're best bet would be to go to a car parts store and buy a battery hygrometer. Use this to check the specific gravity of each cell in the battery. This will give you a true picture of the condition of your batteries. You must wear goggles and you MUST NOT get the battery acid on you or any thing you want to keep.

-- Ace (, November 28, 1999.

farmbeet; Concerning your first question; You can let your batteries go down to 8.4 volts if 12volt battery, 6 volt battery (especially deep cycle are different) They have a longer cold cranking amp rating, so charging them at your setting of 2 or 40 would be enough, NOT 200 amp setting. Why, because your charger at that setting is for quick start on a dead battery. By running the generator for only an hour will probably not be enough to charge your 2-6 volt batteries, I would say at least 2-4 hrs to completely recharge the batteries. You would won't be using that much more fuel, besides it would be better to have a compltely charged battery than none... And if you are using the gen for a water pump,do have a system that can hold water in a tank and it be pressurized.

-- Furie (, November 28, 1999.

Go to and read all about batteries, charging, safety, etc.

-- r.u.reddy (don', November 29, 1999.

these are 6-volt golfcart batteries (essentially deep-cycle)
They don't have a cold-crank rating like automotive batteries.

If you try to completely discharge these batteries, you will wreck them.

It is unfortunate that your charger does not have the ability to bulk charge and then taper off to an absorbtion charge once it reaches full capacity.

-- plonk! (, November 29, 1999.

Deep cycle batteries, such as your golf cart types should ideally be charged at a C/10 rate (C=Battery capacity in ampere-hours divided by 10). This is the accepted wisdom for long term battery happiness. You can charge at a C/5 rate between twenty and fifty percent of charge without shortening the batteries life too much. Then too ideally you will not discharge your batteries more than 50%. 200 amps is totally out of the question anyway, the batts would die fast and it's likely that's a "jump start" setting on the charger (not useful for charging batteries). When left at the 40 amp setting the charger will probably taper somewhat as batt voltage rises.

Batteries are happiest if full every day which is what I attempt to do with mine. In any case they should be full as often as possible. A battery will charge most efficiently when any plate sulfation is "young" (has to do with the crystaline structure of the lead-sulfate).

Minimize battery depth of discharge before recharging, recharge fully as often as possible. There are trade offs which I try to avoid.

Battery voltages are not a good indicator of battery state of charge, at least not a dependable one. I threw my hydrometer away and bought cumulative ampere-hour meters which is the only way to really know what the batts are doing.

Farmbeet, to "Is there anything else I should know" I'd say yes, quite a bit. You'll find some useful files in the download section at our website that will be a large help.

-- Don Kulha (, November 29, 1999.

Thanks everyone for sharing your battery insights and links. It has all been very helpful to me and I hope for others too.

Best wishes


-- farmbeet (farmbeet@12volt.power), December 03, 1999.

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